Gentisic acid and its alkali metal and ammonium salts



Patented Apr. 3, 19 51 GENTISIC ACID AND ITS ALKALTMETAL AND AMMONIUM SALTS Ferdinand B. Zienty, Brentwood, and Dorothy J. Harvey, St. Louis, Mo., assignors to Monsanto Chemical Company, St. Louis, Mo., a, corporation of Delaware No Drawing. Application March 16,1950,

Serial No. 150,102

21 Claims.

This invention relates to 2,5-dihydroxybenzoic acid, or as it is more commonly called, gentisic acid, and its alkali metal or ammonium salts; more specifically, this invention relates to an im proved process for the production of gentisic acid and its alkali metal and ammonium salts.

, The Kolbe synthesis has generally been considered to be a most convenient method for prehydrous alkali metal phenolate was prepared and charged to an autoclave wherein it was carboxylated with CO2. Subsequent investigations revealed carboxylation processes ,could be carried out on an alkali metal phenolate dissolved or suspended in anhydrous inert organic medium. In such a process, the alkali metalphenolate is generally separately prepared by 'reactingZ-an a1 kali metal hydroxide with the ,phenolin the organic medium and stripping off the water formed inthis reaction. In either of these processes, commercially practical yields of the desired hydroxy aromaticcarboirylic acid could be obtained lonly if anhydrous conditions are maintained. The presence of water, either in small amounts as a contaminant'or as the liquid carrier, retarded the reaction so significantly that either no product was obtained or else it was obtained in insignificant yields, depending upon the particular alkali metal phenolate being carboxylated.

In either of the above mentioned processes, there exist some inherent disadvantages. The desirability of maintainnig anhydrous conditions dictates the necessity of preparing the alkali metal phenolate as a separate and distinct step in the process. Furthermore, the maintenance of anhydrous conditions requires careful process control and the availability of dehydration facilities. Carboxylation with considerable quantities of externally supplied gaseous CO2 requires costly equipment and spacious storage facilities. In our copending application Serial No. 94,512, filed May 20, 1949, an improved process for'the production of gentisic acid and its alkali metal and ammonium salts was'disclosed and claimed. As-was pointed out therein, the process disclosed and claimed, which comprises reacting hydroquinone with an alkali metal or ammonium carbonate or bicarbonate in a medium containing water at a temperature in the range of fromabout to about 200 C., and a total pressure in excess of about 200 pounds per square inch, constituted a significant improvement over those proc-' esses disclosed in the prior art in that an excellent yield of gentisic acid could be obtained in a single step process which did not require the maintenance of anhydrous conditions. While that process constituted a most significant advance-'- ment in the art, considerable room for improve ment was still possible. While that process provided for anexcellent yield-of gentisic acid based on recovered hydroquinone, the actual conversion of hydroquinone to gentisic acid, while equal to or superior to that previously obtained in the art, was still relatively low, namely, about 30%; It was further found that the crude gentisic acid obtained from that processcontained a consider able amount of highly colored, tarry side products. While the gentisic acid thus obtained could be purified and an excellent yield of substantially pure material obtained, purification was some what difficult in that repeated recrystallizations were required in order to eventually obtain a white product free from colored bodies. It is an object of this invention, therefore, to provide an improved process for the production of 2,5-dihydroxybenzoic acid (gentisic acid)v and its alkali metal and ammonium salts. It is another object of this invention to provide an improved and highly practical process for the production 'of gentisic acid and its alkali metal and am moniumsalts in increased yields and in increased conversion by the carboxylation of an alkali metal or ammonium salt of hydroquinone, whereinthe formation of the alkali metal or ammonium salt'of-hy'droquinone and its subsequent carboxyl ationare carried out as an essentially single step in the presence of water. Further objects will become apparent from the description of the novel process of this invention and the claims.

It hasnow been discovered-that gentisic acid or its alkali metal or ammonium salts may be obtained in excellent and increased yields by subjecting the alkali metal or ammonium salt of hy droquinone -(para-dihydroxy benzene) to reaction with carbon dioxide in the presence of water and the sulfide ion, at a temperature in the ranged from about 150 C. to about C. and a pressure in excess. of about 200 pounds per square inch.

According to a preferred embodiment of this in-' vention the novel process may be carried out by reacting ,hydroquinone with an alkali metal or ammonium carbonate or bicarbonate in a medium containing water and the sulfide ion, at a temperature in the range of from about 150 C. to about 180 0., and a total pressure in excess of about 200'poundsper'square inch. Under such conditions, it has been found that the alkali metal or ammonium carbonate or bicarbonate reacts with hydroquinone to form the alkali metal or ammonium salt of hydroquinone-iand liberates gaseous CO2 which then acts as a carboxylatinfg agent, thereby converting a much higher percentage of the hydroquinone to tne alkali metal salt of gentisic acid than was heretofore steam able. Thus, according to thenovl proces'softl'iis invention, it is now possible to obtain a 40-50% conversion of hydroquinone to gentisic 'acid.

The following examples are illustrative of the novel process of this invention:

Example I -An iron autoclave was charged wastage-1r hydroquinone, 100 =of potassium bicarbonate, 2 g. otsodium sulfide nonahydrate and 100 m1 of water The autoclavewas then swept "clear oi air with CO2 and an ;i-nitial pressure oilpounds per square inchof Q02 applied. With constant agitation the autoclave was 'heated to l5-170 C and at this temperature the pressure rose to approximately 450 500 :pounds per square inch, at-which temperature and pressure the reaction was -maintained for 12 hours. a V

,Theautoclave was then cooled, Venteda'nd the reaction product removed byallowing the autoclave to drain vand washing the autoclave with 100 ml. of water. The :reactionzmi'xture wasjlthen acidified with hydrochloric acid to apI-I' of 7.0, and the unreacted hydroquinone extracted with butanol. The water layer was then acidified to a ..pH of -l-2 with hydrochloric acid gentisic acid extracted with butanol. Titration of the butano'l layer containing fg'entisic acid indicated that approximately .a 40% conversion hydroquinone to gentisic acid had been (obtained. The 'butanol 'layer containing \gen'tisic acid was then evaporatedto recover the g'entis'ic acid. The recovered Igentisic acid was flthen r'ecrystallized from water, whereby "fine wh'ite needle crystals of gentisic acid. having a melting point of 205-206 C. wereobtained.

The -butanol layer containing the un'reacted hydroquinone previously obtained, was then evaporated and unreacted hydroquinone re"- covered. 'On the basis of recovered "hydro quinone, it was'foundthat approxn ateiyaneoet yield of .gentis'ic acid had been-obtained.

Example :II

'ri1e critical natur o'f the iteinpiature nin'imtions of this reaction was illustrated byrepeatprocedure described in Example I wasirepeated I with the exception 'that the reaction tempera ture was maintained at about 210 'to 215 C. Under 'suchc'ondition's the "yield and quality "of the g'entisic acid "thus 5 obtained "was {significantly lower than that obtained in '--ExampIe I.

and the 4 Example IV 55 g. of hydroquinone, 84 g. of sodium bicarbonate, 1 g. of potassium sulfide and about 220 of water were charged -to an iron autoclave which was then swept. clear er air with CO2. Without applying an initial positive CO2 pressure to the system, the autoclave was closed and heated toabout 175 0., during which time the pressu e rose to "within the preferred pressure range of above 200 pounds per square inch where it was-maintained with continuous stirring for about 12 hours.

The autoclave was then cooled and vented and the gen'tisic acid :separated and purified in the manner described in Example I. The yield of rgentisi'c acid obtained in this case and the conversion of hydroquinone to gentisic acid, were comparable to those obtained in Example I.

Example V Toan iron autoclave equipped with an e'fiicient agitator is charged 55g. of hydroquinone, 53 5g. of sodium carbonate, 2375 g. of sodium sulfide (Na'zS) and about 1-l0 -m1. of-Water.' The system was swept --clear of air with "CO2 and rapidly heated to a temperature of about 180 C. and maintained 'ata pressure of about 550 -pounds p'er square inch by the periodic addition of gaseous tions of butanol.

CO2. After maintaining the reaction mixture at this temperature and the pressure for about 1 2 hours, the autoclave was cooled and vented and an excellent yield of sodium gentisate obtained.

Example VI 55 g. of hydroquinone, 53 'g. "of sodium 'cai bonate, 195 1g. of 'ortho dichlorobe'nzene, 0.5 "g. of sodium sulfide and '30 g. -of Water were c arged to an iron autoclave equipped with an agitator, With continuous stirring the autoclave was swep't free of air with CO2, a booster charge of I50 pounds per square inch of COzpr'essure applied, and the autoclave heated rapidly to about 175 "C Thepressure'was raised and maintainedatfabout 450-500 pounds "per square inch "for a total 5r l'z s .7

The autoclave was cooled andvente'd andthe reaction mixture washed with "400 ml "o'f wate'r. The mixture was f ltered, and on standing, the filtrate separated into an organic layer a'n'd' 'an aqueous layer. The water layer was separated and "acidified withsul'furic acid to a ofaboiit 2L5 and then extracted with three ml. por- I "The butariol extract treated with a saturated solution of sodium bicarbonate. The butanolfllayer was 'ev'ap'orated to recover the unreacted hydroquin'one. The water layer containing the sodium salt of gentis'icacid was again acidified to ap'H of about 215 and extracted with butanol. 'The butanol was evap'ofrated, thereby obtaining crude .gentisic acid which was then purifiedi-by recrystallization from water obtaining an excellent :yield of fine white crystals of gentisic-acid=having amelting point of 205110 206 C. I

' Example VII The critical nature of the temperature-limitations of :this reaction was again illustrated by repeating the procedure' described in :Example with the'exception that the-reaction temperature was maintained at about 1B5 *C. In this-case fan impractical low conversion of :hydroiquinone was obtained..:' a

' by the periodic addition of gaseous CO2.

" 7 Example VIII As further illustration of the critical nature of the temperature limitations of this reaction, the

procedure described in Example VI was repeated Example IX The procedure described in Example VI was repeated with the exception that the liquid medium contained 195 g. of ortho-dichlorobenzene and g. of water. J In this case the yield and quality of the gentisic acid thus obtained was si nificantly lower than that obtained in Example Example X m 5- An iron autoclave was charged with 55 g. of hydroquinone, '84 g. of sodium bicarbonate, 200 g. of butanol, 5.5 g. .of sodium sulfide and 80 g. of water. The autoclave was swept free of air with CO2 and then without applying an initial positive CO2 pressure to the system, the autoclave was closed and heated to about 1'70? 0., during which time the pressure rose to within the prescribed pressure range of above 200 pounds per square inch where it was maintained withcon- Example XI 110 g. of hydroquinone, 138 g. of potassium carbonate, 5 g. of potasium sulfide, 125 g. of toluene and 125 g. of water were charged to an iron autoclave equipped with an efiicient agitator. The

system was swept clear of air with CO2 and rapidly heated to a temperature of about 160 C. The pressure was allowed to rise and maintained at a pressure of about 7.00 pounds per square inch After maintaining the reaction mixture at this temperature and pressure for about 14 hours, the autoclave was cooled and vented, thereby obtaining an excellent yield of potassium gentisate and an .7

Example XII An iron autoclave was charged with 55 g. of hydroquinone, '75 g. of ammonium bicarbonate, 200 g. of butanol, 1.5 g. of sodium sulfide and 75 g. of water. The autoclave was swept free of air with CO2, and then without applying an initial positive CO2 pressure to the system, the autoclavewas closed and heated to about 170 C., during which time the pressure rose to within the prescribed range where it was maintained with continuous stirring for 14 hours. After, cooling and venting the autoclave, gentisic acid was sepa: rated and purified in the manner described in Example VI.

Example XIII 110 g. of hydroquinone, 114 g. of ammonium carbonate, (NI-I4) 2CO3.H20, 130 g. of toluene, .55 g. of sodium sulfide and 110 g. of waterwere charged to an iron autoclave. The system was swept clear of air withCOz and then rapidly heated to a temperature of about 180 C. with constant agitation. The pressure was allowed to rise and maintained at a pressure of about 650 pounds per square inch by the periodic addition of gas- 6. eous C02. After maintaining the reactionmix-i ture under these conditions for about 15 hours, the autoclave was cooled and vented and an ex-- cellent yield of ammonium gentisate recovered.

Example XIV g. of hydroquinone, 200 g. of potassium bi-'- carbonate, g. of toluene, 5 *g. of potassium sulfide, and about 115 g. of water were charged to! an iron autoclave. The autoclave was closed and heated to about 180 C. during which timethe pressure rose to within the prefered pressure range where it was maintained with continuous stirring for about 14 hours.

After the reaction was complete, the autoclave was cooled and vented and an excellent yield of potassium gentisateobtained.

. Example XV An iron autoclave was charged with 110 g. of hydroquinone, 168 g. of sodium bircarbonate, 5 g. of sodium sulfide, 400 g. of ortho-dichlorobenzene and g. of water. The autoclave was closed and thenheated to about C. with continu-' ous stirring. The pressure rose to within the prescribed pressure range where it' was maintained for about 15 hours.

After this reaction period, the autoclave was cooled and vented and the gentisic acid separated and purified in the manner described in Example VI.

Example X VI The procedure described in Example I was repeated utilizing ammonium sulfide in place of the sodium sulfide nonahydrate. An excellent yield of substantially pure gentisic acid was obtained.

Example XVII lent yield of substantially pure gentistic acidfwas obtained.

Example XVIII The procedure described in Example VI was repeated utilizing ammonium sulfide in placeof the sodium sulfide. An excellent yield of sub.- stantially pure gentisic acid was obtained.

Example XIX The procedure described inv Example VI was repeated utilizing 0.5 g. of H25 in place of the 0.5 g. of the sodium sulfide. The 0.5 g. of ;H2S was incorporated into the reaction mixture bybube bling I-IzS gas through the reaction mixture until the prescribed quantity had been absorbed. An excellent yield of substantiallypure gentisic acid was obtained. .;While specific reactants, quantities of. reactants, temperatures and pressures have been set forth in the preceding examples, various phasesof the novel process of this invention are subject to substantial variation. For example, the presence of the sulfide ion in the reaction mixture may be accomplished by incorporating into the reaction, mixture any of the Well known compounds con: taining a sulfide ion. Typical of such compounds are the alkali metal sulfides, such as sodium, potassium and lithium sulfides, ammonium sul fide, hydrogen sulfide, calcium sulfide, ma nesium sulfide, manganic sulfide, manganous sulfide, and the various acid sulfides, such as, for

- tageously.

7 example; the sodium. potassium. lithium, masnesium and calcium acid, sulfides. Theuse of the alkali, metal sulfides, ammonium sulfide and hy-..

drogen sulfide, constitute a preterred embodiment of this invention. The quantity of the sulfide ion utilized in the novel process of this invention may lie-varied ever a substantiali range.

Aslow as 0.000l% and ashigh as 50% or higher. by weight based on hydroquincne, of the sulfide ion containing compound may be fused adyan From a practical standpoint, hOXS/e ever, there is little advantage to be gained in utilizing quantities of the sulfide ion containin compound in excess of by weightbased on the Lhydroquinone.

In this: process, the COauSEd to .carboxylate the alkali metal or ammonium salt. of hydro: quinone may be autogenetically obtained from the initial reaction and the pressure autogeneti: cally maintainedwithin the prescribed range. It is not essential, however, that this reaction be carried out under strict autogenetic conditions, as "the CO2 obtained from the initial reaction between the alkali metal or amen-minimv carbonate or bicarbonate and "hydroquinone may, in order to speed the reaction, be augmented by the introduction of CO2 from an external source :of supply.

In carrying out the novel process of in-. ventionyi-t is preferred that approximately :2 molecular equivalents of the alkali metal or ammonium carbonate or bicarbonate be utilized for each molecular equivalent of hyditoquinone. Thus, inv the case of the alkali metal .01" am--. monium. bicarbonate, approximately 3 .mols of the alkali metal or ammonium bicarbonate should be utilized for each mcl of hydroquinone. In the case of the alkalimetal-or ammonium carbonate, approximately 1 mol of the alkali metal or ammonium carbonate should be utilized for each mol of hydroquinone. While stoic'hiemetri- .cal proportions of these reactants prefered, these exact proportions of reactants, however, are not of. a criticalcnature from the standpoint of this invention.

While the reaction must be carried out in liquid medium, the quantity of liquid medium to be utilized is governed more by the nature of the equipment rather than hy't-he chemistry of the such instances, it is preferred that the liquid .In'edium contain at least about 10% by weight of water. The balance of the medium may be any of the commonly used liquid organic solvents. For example, there may be used butanol, toluene,

decahydronaphthalene, many of the natural gasoline :fac'tions, such as the one boiling in the range of from about 150 to 205 0., benzene, chlorobenzene, ortho dichlorobenzene, and xylene. In such aliquid reaction medium,.a con-= .centration of Water of less thanabout 10% by weightsignificantly reduces the amount of hy- "d flqu n nn rted o zeentis c and As th For example, the liquid. ,medium water content in such a medium is increased bey n 5 y we ght t e c n ersion. oi hydr quinon a p ar to ec ase to so e extent ii i. t on en ti Q Wat r be in o ppr h 1.0 a which ti c a ed y elds'ofms-e c e a ainst realized- T us. it is r red in a medium made of water only in part that the concentration of water he maintained within the range of from about 10% to about 59% by; weight.

The temperature limitations of this reaction are qui -c i ical, and mus bemain a nedv i th rang of from a flu t 3 e fi fi and below this temperature range significant losse in yield are enc untered Sim l rl the p es mus b aint in d n exce soi bout i P521 per square i ch...and prefe ably thin he: of from about 300 to 1,000 pounds per square inch, However, pressures. of the order of 5,000 pounds per square inch may be utilized. As mentioned hereinbefore, this pressure may be maintained a-utogenetically or the-CO2 supply obtained item the formation of the alkali metal or ammonium salt of hydroquinone, augmented by the introduc: tion of CO2 from an external source .of supply, While the reaction proceeds quite satisfactorily under autogenetic conditions, it has been foundto be somewhat advantageous to apply. an initial booster charge of about 1-50 pounds per square inch pressure of CO2. This booster charge --:Ea.-; cilitates the starting of the reaction, after which time the pressure may be maintained :autogenetically. It is alsoposs-ible'to begin the reaction under autogenetic conditions, and then supply additional CO2 in order to raise the pressure Within the prescribedrange of above 200 pounds p qua ch.-

The time for the completion of: the carboigyla tio n reaction varies considerably with the nature of the equipment, method of agitation and the pressure and temperature utilized. General-l y,-the reaction is completed within from -'8 to 16 hours;

After carboxylation, the crude alkali metal or ammonium salt of gentisic acid may be recovered by any of the convenient-methods -we1lgk-newn to those-skilled in theart. Asa result ofthis inve tion, it has been found that the ;reac-tion ture thus obtained contains a smallerguantr of tarry, highly coloredside products as contami nants of the crudealkalimetal orammonium'salt of gentisic acid obtained. For this reason, purification orthe crude e ct on pro uct o tain sie cord tov the n vel p ocess .of this in entio is more readily c ompl sh d- .Af e r the n actesl e n ha e bee em ed f om t ereacdoa pr d n cr stall z tiqn o t e a a i or ammon i rn sal o een isic acid ieusual, that is r qu red mu de t phteina hi ecmstak line-product. I'fdesired,ithealkal metnl m.- monium'salt-may be converted to lgentisic acid-by. acidification and agentisic acid recoyeredzdirectly. Here again, one recrystallization is :usually cientto produce 'a'whi'te crystalline material".

What is claimed is: t

1. In a process for the preparation of 2,5- dihydroxyebenzoic acid and its allrali ,metal and ammonium salts, :thestep comprising reap... g4?- compound selected from :the :group yQQIlSl-Slilllg 9f he alkalimetal and -:ammonium sal 1 f mar-pqui-non with carbondiox i the presence 59 t nd h ulfi ioaa a tempe atu e a pr ssu n e cess of =a 11 .2i1 mounds square inch.

9 r f 2."In:"a Tprocessifor the'preparation of 2,5- dihydroxy-benzoic acid and its alkali metal and ammoniumfsalts, the" step comprising reacting -'hydroquinone with a compound selected from the group consisting ofthe alkali metaland ammomum carbonates and bicarbonates, in the presence of water and the sulfide ion at a temperature in the range of from about 150 C. to about 180 C. and a pressure in excess of about 200 pounds per square inch.

3. In a process for the preparation of 2,5- dihydroxy-benzoic acid and its alkali metal and ammonium salts, the step comprising reacting hydroquinone with a compound selected from "the group consisting of the alkali metal and ammonium carbonates and bicarbonates, and carbon dioxide in the presence of water and the sulfide ion, at a temperature in the range of from about 150 C. to about 180 C. and a pressure in excess of about 200 pounds per square inch.

In a process for the preparation of 2,5

dih'ydr'oxy-benzoic acid and its alkali metal and aminonium salts, thestep comprising reacting hydroquinone with a compound selected from the group consisting of the alkali metal and ammonium carbonates and bicarbonates in water and "group consisting ofthealkali metal-and.- ammonium carbonates and bicarbonates in water, andin the presence of carbon dioxide anda com.-

,pound selected from the group consisting of'the falkalimetal sulfides; ammonium sulfide and hydrogen sulfide, at a' temperature in the range of from about 150C. to about 180 C. and a pressure in excess of about 200 pounds per square inch.

In a process for the preparation of 2,5-dihydroxybenzoic acid and its alkali metal and ammonium salts, the step comprising reacting hy-" droquinone with a compound selected from the group consisting of the alkali metal and ammonium carbonates and bicarbonates in water, and in the presence of carbon dioxide and an .alkali metal sulfide, at a temperature in the range of from about 150 C. to about 130 C. and a pressure in excess of' about 200 pounds per square inch;

hydroxybe'nzoic acid and its sodium salt, the step comprising reacting hydroquinone with sodium bicarbonate in water, and in the presence of carbon dioxide and an alkali; metal sulfide, at a temperature in the range of from about 150 C. to about 180 C. and a pressure in excess of about 200' pounds per square inch.

8. In a process for the preparation of 2,5-dihydroxybenzoic acid and its potassium salt, the step comprising reacting hydroquinone with p0 .tassium bicarbonate in Water, and in the presence of carbon dioxide and an alkali metal sulfide, at a temperature in the range of from about 150 C. to about 180 C. and a pressure in excess of about 200 pounds square inch.

9.11m process for the preparation of 2,5-dihydrox rbenzoic acid and its potassium salt, the

step coirrprising reacting hydroquinone With potassifc' carbonate in water, and in the presence of carbon dioxide and an alkali metal sulfide,

7-: Inla process for the preparation of 2,5-di-,

:about200 poundsper square inch.

at atemperaturein the range of from about 150.?

C. to about 180 C. and a pressure in excess 9i.

' .10. In a process for the preparation of 2,5 6.1

hydroxybenzoic acid and its alkali metal and a nmonium salts, the step comprising reacting hydroquinone with a compound selected from the group consisting of the alkali metal and ammonium carbonates and bicarbonates in water, and in the presence of carbon dioxide and'am- .monium' sulfide, at a temperature in the range "of from about 150 C. to about 180 C. and a pressure excess of about 200 pounds per square inch.

11; In a process for the preparation of; 2,5-dihydroxybenzoic acid and its alkali metal and am.-

monium salts, the step comprising reacting hydroquinonewith a compound selected-- from the group consisting otthealkali metal and ammonium carbonates and bicarbonates in water,

and in the presence of carbondioxide andhydrogen sulfide, at a temperature in the range of from about,15 0 C. to about 180 C. at a pressure in excess of about 200 pounds per square inch.

12. 'In a process for the preparation of 2,5-dihydroxybenzoic acid and its alkali metal and ammonium salts, the step comprising reacting hy- :droquinone with a compound. selected fromthe group consisting of alkali metal and ammonium carbonates and bicarbonates in a liquid medium containing an organic solvent and at least- 10% by Weight of water and in the presence of carbon dioxide and; the sulfide ion, at. a temperature in the 'range offrom about 150 C, to about 180E 0 and a pressure in excess of about 200 pounds per 13. In the processi for ther'bmtnn of 2,5-dihydroxybenzoic; acid and its alkali metal and ammonium salts, the step comprising reacting hydroquinone-witha compound selected from the group'consistingof the alkali metal and 1 am- .monium carbonates and bicarbonatesin a liquid medium containing an organic solvent and from hydroquinone with a compound selected from the group consisting of the alkali metal and ammonium carbonates and bicarbonates in a liquid mediumcontaining an organic solvent-and from about 10% to about by weight of water in the presence of carbon dioxide and a, compound selected from the group consisting of the alkali metal sulfides, ammonium sulfide and hydrogen sulfide, at a temperature in the range of from about C. to about C. and a pressure in excess of about 200 pounds per square inch;

15. In a process for the preparation of 2,5-dihydroxybenzoic acid and its alkali metal and ammonium salts, the step comprising reacting hydroquinone with a compound selected from the group consisting of the alkali metal and ammonium carbonates and bicarbonates in a liquid medium containing ortho-dichlorobenzene and from about 10% to about 50% by weight of water in the presence of carbon dioxide and a compound" selected from the group consisting of the alkali metal sulfides, ammonium sulfide and hydrogen sulfide, at a temperature in the range fj sure in excess of inch;

. 1 1 about 200 pounds per square 10. .In a process for the preparation of '2;5-.di h-ydrox ybenzoic acid and its alkali metal and ammonium salts, the step comprising vreacting hydroquinone with a compound selected from the group consisting-of the alkali metal and ammonium carbonates and bicarbonates ma liquid medium containingbutanol and from about 10% toabout 50% by weight of water in the presence of carbon dioxide and acompound selected from the group consisting of the alkali metal sulfides, ammonium sulfide and hydrogen sulfide, at. a temperature in the range of from about 150 C. to about180 C. and a pressurein excess of about 200 pounds per square inch. v

1'7. Ina process for the preparation. of 2,5-dihydroxybenzoio acid and its alkali metal and ammonium salts, the step comprising reacting 'h-ydroquinone with a compound selected from the group consisting of the alkali metal and am.- monium carbonates and bicarbonates in a liquid medium containing 'butanol and from about 10% to about 50% by Weight of water in the presence of carbon dioxide and an alkali metal sulfide, at a temperature in the range of from about 150 C. to about 180 C. and a pressure inexcess of about 200 pounds per square inch.

18. In a process for the preparation of 2,5-d-ihydroxybenzoic acid and its sodium salt, the step: comprising reacting hydroquinone with sodium bicarbonatein a liquid. medium containing butanol and from. about 10% to about'50% by :weig ht oi water in the presenceof carbon dioxide and an alkali metal sulfide, at a temperature ,inthe range of from about 150 C. to about 1802 C. and a pressure in excess of about 200 pounds per square inch.

'19. In a process for the preparation of 2,5-dihydroxybenzoic acid and its potassium salt, the step-comprising reacting 'hydroduinone with ptassium bicarbonate in a liquid medium contain- :ingbutanol and from about to about byweight of Water in thepresence of carbon dioxide and an alkali metal sulfide, at a temperature in the range of from about C. to about ;1'801 C. and a vpressure in excess or about 1200 pounds persquareinch. V

'20. In a process for the preparation .of2,5-.di"- 'hydroxybenzoic acid and its potassium salt, the step comprising reacting hydroquinone with poxtassium carbonate in a liquid medium contain.- ing 'butanol and from about 10% to about.50% by'weight of waterin the presence of carbon (ii:- oxide and an alkali metal sulfide, at a temperature in the range of from about 150 C. to about C. and a pressure in excess :of about 200 pounds .per square inch. 21. In a-process for .the preparation of. 2.5-d1- ,hydroxybenzoic acid. and its alkali metal and ammonium :salts, the step comprisin'grrieacting hydroquinone with .a compound. selected from the group consisting of the alkalimetal and ammonium carbonates andbicarbonates in aliquid medium containing butanol and .from about 10% to about 5.0%- vby weight-of water in the presence of carbon dioxide and ammonium sulfide, at a temperature in the range offrom about-150 C.

to about 180 C. and a pressure in excess of about .200 :pounds per square inch.

FERDINAND B. ZIENTY. DOROTHY .J. HARVEY. j

REFERENCES CITED The following references are of record in. the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Drechsel, Ze'it' f-iir Chemie, 8' Jahrg. 1865, pp. 580-581. Senhofer et a-L, Beilstein ('Handbuch, 4th ed.) vol. 10; pp. 377, 384 (1927). 

1. IN A PROCESS FOR THE PREPARATION OF 2,5DIHYDROXY-BENZOIC ACID AND ITS ALKALI METAL AND AMMONIUM SALTS, THE STEP COMPRISING REACTING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE ALKALI METAL AND AMMONIUM SALTS OF HYDROQUINONE WITH CARBON DIOXIDE IN THE PRESENCE OF WATER AND THE SULFIDE ION, AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 150* C. TO ABOUT 180* C. AND A PRESSURE IN EXCESS OF ABOUT 200 POUNDS PER SQUARE INCH. 